Flashcards in NEETS Mod 5 - AC Generators Deck (24)
What are AC generators generally known as?
What principle do all electrical generators depend upon?
What are the two ways EMF is induced in a coil?
(1) a coil cutting through a magnetic field
(2) a magnetic field cutting through a coil
Magnetic Induction occurs when there is relative motion between what two elements?
Conductor and magnetic field
What is the part of an alternator in which the output voltage is generated?
What are the two basic types of alternators?
What is the main advantage of the rotating field alternator?
Output voltage is taken directly from the armature (not brushes or slip rings)
What are the two types of rotors used in rotating-field alternators?
When is a turbine-driven rotor used?
When the prime mover is a high speed turbine.
When are salient-pole rotors used?
In low-speed alternators
How are alternators usually rated?
By the voltage and maximum current they are designed to produce. (volt amperes)
What type of prime mover requires specially designed high-speed alternator?
Salient-pole rotors may be used in alternators driven by what types of prime movers?
Low speed (portable tools & small appliances)
What does single phase indicate?
One continuously alternating voltage (output)
What is the most common alternator used today?
What determines the phase relationship between the voltages in a two phase AC generator?
Placement of the armature coils
In a three phase alternator, what is the phase relationship between the individual output voltages.
Each phase is displaced 120°
What are the two methods of connecting the outputs from a three phase alternator to the load?
Delta & Wye
What type of transformers and connections are used to convert 450v, 3 phase power to 117v, single phase?
Single phase, step-down transformer
What two factors determine the frequency of the output voltage of an alternator?
Number of poles (NP), multiplied by
Speed of rotation, divided by 120.
What is the frequency of the output voltage of an alternator with four poles that is rotated at 3600 rpm?
4 × 3600 = 14,400
14,400 ÷ 120 = 120
The variation in output voltage as the load changes is referred to as what? How is it expressed?
Percentage of regulation
How is output voltage controlled in practical alternators?
By varying the voltage applied to the field windings.